The invention is an improvement on the invention disclosed in my U.S. Pat. application, Ser. No. 505,824, filed on Sept. 13, 1974. As there shown, an ultrasonic transducer is coupled to a test specimen by means of a liquid couplant supplied to the transducer from a remote source. The sensitivity of the apparatus is affected by the ability of the liquid couplant to transmit pulse energy between the specimen surface and oscillatable transducer element (piezo electric crystal or coil-diaphragm element). In the arrangement described in my aforesaid application Ser. No. 505,824, a coupling liquid is caused to continuously seep through a porous membrane locatable at the specimen surface, thereby forming a liquid film thereon; mechanical wave energy is transmitted to and/or from the specimen surface via the liquid film.
For best results the porous membrane should be sized and contoured so that it can take a position fairly close to the specimen surface; otherwise the liquid couplant will not effectively perform its energy-transmitting function. If the porous membrane has a relatively small exposed face area, it will accommodate itself to depressions or convex surfaces found on many test specimens (such as engine blocks, valve bodies, tire carcasses, gears, etc). However the membrane will then not be especially suited for scanning large surface areas such as are found on large sheets, vehicle hulls, etc.
The present invention proposes a transducer arrangement comprising a single transducer head and a plurality of different liquid applicator heads. Each applicator head is equipped with a porous membrane having a size and surface contour suited to scan a specific type of surface; e.g., a large flat surface or a small curved area (concave or convex.) The applicator heads are interchangeably usable with a single common transducer head. The invention enhances the usefulness of the transducer assembly while reducing its total cost.